1. Field of the Invention
This invention relates to reclaiming europium-activated yttrium oxysulfide phosphors contaminated with other cathodoluminescent phosphor materials. More particularly it relates to a process for removing the contaminants and additionally enables the particle size, emission color, body color and the chemical composition of the resulting phosphor to be controlled in such a manner as to yield a highly satisfactory cathodoluminescent europium-activated yttrium oxysulfide phosphor.
2. Prior Art
Europium-activated yttrium oxysulfide phosphor is one of the most used red emitting phosphors in color picture tubes. Another red emitting phosphor used in sizeable quantities is europium-activated yttrium oxide. However, in many instances due to poor quality tubes, tube breakage and the like, these phosphors become contaminated with other phosphors. Since these rare earth phosphors are expensive recovery or reclamation is necessary for economic reasons. Generally the red emitting phosphor has also been contaminated with the blue and green emitting phosphors which are generally the zinc sulfide or zinc-cadmium sulfide. Heretofore, the contaminated red rare earth phosphors have been reclaimed by treating with mineral acid washes, caustic washes and with or without oxidizing agents such as hydrogen peroxide and sodium hypochlorite. Such treatment is adequate for many types of reclaims, however when a europium-activated yttrium oxysulfide phosphor has an appreciable amount of yttrium oxide along with the other cathodoluminescent phosphors; the methods used to remove the blue and green contaminants dissolve some of the yttrium oxide europium-activated red phosphor. Since the rare earth materials are very expensive, this adds appreciably to the cost of the phosphors. Additionally, even if the yttrium oxide is not lost, the chromaticity of the reclaimed phosphor may be shifted because the europium that is present in the europium-activated yttrium oxysulfide. It is believed that a method which enables the treatment of a contaminated europium-activated yttrium oxysulfide phosphor wherein the contaminants include europium-activity yttrium oxide along with the other cathodoluminescent materials used in color picture tube manufacture in which the europium-activated, yttrium oxide material is converted to a satisfactory europium-activated yttrium oxysulfide having a desired or predetermined yttrium to europium ratio would be an advancement in the art.